The effect of evolution of rock asphalt subjected to high temperature and high pressure on the mechanical properties of oil well cement

In this paper, the structural evolution of natural rock asphalt and rock asphalt treated with liquid nitrogen subjected to high temperature and high pressure (HTHP) were studied, and then its influence on mechanical properties of oil well cement was investigated. The results show that the pyrolysis reaction of rock asphalt was promoted by HTHP, which occurred at 320 ℃ at normal pressure and appeared at 180 ℃/20.7 MPa. The pores in the particles caused by the pyrolysis of rock asphalt were healed with the extension of curing time, and the interface bond between rock asphalt and cement matrix was improved. Rock asphalt has a good toughening effect on cement paste, especially treated rock asphalt. •High temperature and high pressure promoted the pyrolysis of rock asphalt.•The rock asphalt treated by liquid nitrogen can enhance the toughness of cement stone under HTHP.•The interface bond between rock asphalt and cement matrix was gradually improved with the extension of curing time.